Diffs name their chain; history shows the ruleset's diff

The ruleset's diff names the chain each hunk is in on its @@ line, as
git names the function. A history entry shows what it did to the
ruleset (web page, hc history diff, GET /history/{id}/diff), rebuilt
from the current configuration by stepping back through the later
entries. A changed setting is listed by its own fields
(builtins.drop_invalid) instead of the whole object.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -103,6 +103,18 @@ All notable changes to Housecarl are documented here. The format follows
 
 ### Changed
 
+- The ruleset's diff (Changes, `hc changeset diff`, `--dry-run`) names
+  the chain each part is in on its `@@` line (`@@ -40,6 +40,8 @@ chain
+  forward`), as `git diff` names the function, so a rule added deep in a
+  long chain says whether it is in input, forward or output.
+- **History shows the ruleset's diff.** An entry's page (and `hc history
+  diff ID`, `GET /history/{id}/diff`) shows what the change did to the
+  ruleset, for entries made before this version too: the configuration
+  before and after it is got back from the current one and rendered by
+  this version.
+- History lists a changed setting by its own fields
+  (`builtins.drop_invalid: false → true`), on the web page and in `hc
+  history show`, instead of the whole `builtins` before and after.
 - Set names starting with `ban_` are now reserved (`set_name_reserved`):
   ban lists' sets use them.
 - **Rules read as a direction.** A match's zones are written `lan → wan`,